Large scale breeders who supply fish shops with their bettas purposely cross breed different lines until it is a spider-web like jumble of genes in each and every betta. There will be plenty of "surprises," unpredictable colors in the fry, and random tail types (which has taken breeders decades and decades to create) and most importantly- deformed fry. Because of the sporadic and mass scale breeding, deformed and weak fry grow into deformed and weak adults. (Not all, of course, but a large number within a single spawn.) This brings me to the culling, I find it interesting how you say

"By keeping every single fry-you are not doing yourself nor the line you are working with any favors......
One of your goals should be quality not quantity"

That's the stickler- quality, not quantity.
Low quality x low quality = low quality.
High quality x high quality = high quality.
The number of fry that need to be culled from a good pair is far less than that of a pet store pair. Most novice breeders don't even want to cull their first fry, let alone even know what to look for when culling. This leads to deformed fry living a miserable life, and again, weak adults.

I agree 100% that it is a great experience, and that people should be responsible with it. That's why good quality stock is probably the most important step you'll take in preparation of this hobby. It takes as much energy, space, time, water, supplies, money and patience to breed low quality as it does high quality. You can also make a profit on higher quality- not so with pet store offspring.

I'm gonna have to agree with OFL and I have breed petstore fish the only thing I can possibly add to OFL is if ur going to attempt a project make sure u have homes for the new life you are bring in or cull hard.

I think the only time this does not apply is when you are looking for the "Old" genetics, like the true red {Non Cambodian} or the Traditonal Cmabodians, which many are only left in Veiltail form.....for tha matter Oriental black which is really a butterfly or Blacklace...do you want to know why these are endagered?
I can tell you in a one word IBC, the standards they put on to achieve the best and darkest black or red without black edges has a direct effect on wha is being bred, so the strains of yesteryear are super hard to get a hold of as a result, instead, if they showed the very best of what a strain could be and recognised true patterns such as mustard gas and salamander..which by the way will breed true perhaps we would have better quality fish as a whole.
And I can tell you this I was a member in the early years and the only thing that has changed is the diminishing of strains as a result of the people who make decisions as to what is a fault and what isnt, a real good example is the feather tail....who was the genius that called this a fault?
For this craft to grow, it has to progress and evolve oterwise it will stagnate, and the same old crap will be seen year after year, perhpas I will renew my membership...when there is a such thing as The Dragon class...which by the way gets lumped into the bicolor category that is already WAY overloaded..seems if a fish has more than one solid color, this is what is done, instead of recognising strains.....wow....that is a sad way to do things.... I understand the need for money, perhaps if they made specific shows for specific STRAINS that would be an excellent start for this oragnisation to grow, then perhaps we could see the very best Melano, the very best Black lace etc etc..when those changes come and ther are classes for fins types, I will break my fingers trying to get the check book out...so in the meantime Veiltails will get a bumb rap everytime.
I do however agree with the fact many breeders have culls and most will give them to you for shipping the genetics are there one sister just may be homley one of the bunch, bt her daughters may produce real beautys..after all she has the same genes as her beautiful sister..so culls are a very good way to get superior fish.